1. Field of the Invention
The present invention relates to methods and compositions which enhance the epithelial transport of drugs (including peptides, oligonucleotides, proteins and conventional drugs) that are subject to extensive breakdown within epithelial cells in various mucosal sites, such as the gastrointestinal tract. Particularly, the methods and compositions enhance the transport of drugs in most therapeutic categories, such as anti-infective, antiviral, centrally acting, cardio-vascular, respiratory, cholesterol reducing, anticancer, imaging, antidiabetic, immunomodulating, antineoplas-tics, anti-inflammatory, oral contraceptive and the like, across epithelial cells. More specifically, the present invention is directed to using a peptide of at least 2 amino acids, preferably of two to five amino acids. The N-terminal amino acids are preferably Pro-Leu, having a protective group, such as phenylazobenzyloxycarbonyl (Pz-group, ##STR1## ) N-methyl, t-butyloxcarbonyl (t-Boc), fluoroenylmethyl-oxycarbonyl (FMOC) or carbobenzoxy (CBZ), at the N-terminus. If the peptide has more than 4 amino acids, a charged amino acid such as Arg, Lys, Glu or Asp at the C-terminus, transiently and reversibly enhances the transport of drugs across epithelial cells. The mechanism is believed to involve increasing the permeability of tight junctions between epithelial cells through activation of ion transport channels, such as sodium channels on the cell membrane. The protected peptide can be used alone or in a mixture to enhance the transport of drugs across the epithelial cells.
More specific objectives and advantages of the invention will hereinafter be made clear or become apparent to those skilled in the art during the course of explanation of preferred embodiment of the invention.
2. Description of the Prior Art
The entry of high molecular weight active agents (such as peptides, proteins and oligonucleotides) and conventional drugs (such as mannitol, atenolol, fluorescein, insulin, vasopressin, leucine enkephalin, Asu-eel calcitonin, 5-fluorouracil, salicylamide, .beta.-lactones, ampicillin, penicillins, cephalosporins, .beta.-lactamase inhibitors, quinolones, tetracyclines, macrolides, gentamicin, acyclovir, ganciclovir, trifluoropyridine and pentamidine) through mucosal routes (such as oral, nasal, pulmonary, buccal, rectal, transdermal, vaginal and ocular) to the bloodstream is frequently obstructed by poor transport across epithelial cells and concurrent metabolism during transport. Penetration enhancers (substances that facilitate the transport of solute across biological membranes) have been well investigated for the last five decades as reported by Lee et al. (Vincent H. Lee, Akira Yamamoto, and Udaya Bhaskar Kompella, Critical Reviews in Therapeutic Drug Carrier Systems, Vol. 8, No.2, pp. 91-192 (1991), the disclosure of which is herein incorporated by reference). Penetration enhancers are broadly divided into five groups: (1) chelators, e.g. EDTA; (2) surfactants, e.g. sodium lauryl sulfate; (3) bile salts and derivatives, e.g. sodium deoxycholate; (4) fatty acids and derivatives, e.g. oleic acid; and (5) non-surfactants, e.g. unsaturated cyclic ureas. While the penetration enhancers enhance the permeability of the epithelial cell, thereby facilitating the transport of drugs across biological membranes, they also raise a number of pressing safety concerns, such as irritation of mucosal tissues, damages in the mucosal cells, poor damage recovery rates and alterations in mucociliary clearance (Lee et al. at p. 140).
Other approaches, such as co-administration of protease inhibitors, e.g. bacitracin, aprotinin, amastatin, bestatin, and puromycin (Lee et al. at p. 92), modification of peptide, protein and antibodies structures, (U.S. Pat. No. 5,004,697 to Pardridge), and the use of formulations changes, such as pH, tonicity and the use of solubilizers (Lee et al. p. 167) have been reported. In addition, iontophoresis (transfer of ionic solutes through biological membranes under the influence of an electric field) (Lee et al. at p. 163), phonophoresis or sonophoresis (use of ultrasound to enhance the absorption of various therapeutic agents across biological membranes notably the skin and the cornea) (Lee et al., at p. 166) and optimization of vehicle characteristics relative to dose deposition and retention at the administration site (Lee et al., p. 168) have also been tried to enhance the transport of drugs across mucosal sites.
Although these approaches have experienced some success, they have not been entirely successful, either because of safety concerns (e.g. use of existing enhancers), or because they involve ineffective, inefficient, inconvenient and difficult techniques in various applications (e.g. chemical modifications, iontophoresis and phonophoresis). In addition, these approaches failed to protect, specifically, peptide and protein drugs from proteases beyond the lumen if the drug is administrated through the oral route.
There presently is a great need to provide convenient and simple methods and compositions to enhance the epithelial transport of drugs at various mucosal sites. It is desirable that such new methods and compositions provide for a simple, convenient, practical and optimal introduction of drug transport and delivery across epithelial cells at various mucosal sites with as few safety concerns to the patient as possible.